Civil Engineering Reference
In-Depth Information
By inspection, the turndown slabs do not provide enough stiffness to fix the base of the
portal pier sections.
Try an 8
″
Deep by 16
″
Wide Footing With an 8
″
Thick by 12
″
Deep Stem Wall
(See Fig. 13.9)
8126 81616
812816
( () ( ()
() ()
+
+
y
=
=
11 714
.
′′
C
=
82
.
9
′
2
812
12
()
3
16 8
( )
3
I
G
=
8125714
( (.
)
2
+
816429
(
)(
.
)
2
+
+
=
7320
in
4
12
2
E
CG
= 20 862 000 000
,
,
,
lb-in
EI
EI
20 862 000 000
2 660 364 000
,
,
,
CG
WG
=
=
7841
.
<
0
∴N.G.
,
,
,
Try an 8
″
Deep by 16
″
Wide Footing With an 8
″
Thick by 16
″
Deep Stem Wall
(See Fig. 13.9)
8168 81620
816816
( () ( ()
() ()
+
+
y
=
= ′′
14
C
= ′′
10
2
816
12
()
3
16 8
12
()
3
I
G
=
8166
( ()
2
+
8166
( ()
2
+
+
=
12
,, 629
in
4
2
E
CG
= 35 993 600 000
,
,
,
lb-in
EI
EI
35 993 600 000
2 660 364 000
,
,
,
CG
WG
=
=
13 52
.
>
10
∴
OK
,
,
,
The foundation should be similar to the 12″ or 16″ deep foundation walls shown in
Figs. 13.9 and 13.10 to provide the necessary stiffness to create the effect of full fixity for
the piers.
Example 13.1: Portal Frame Foundation Review
The frame shown in Fig. 13.11 is a single-story portal with a wall height of 10′ and pier
widths of 16″. In accordance with APA TT-100B, the recommended maximum lateral
force at each pier is 600 lb (ASD). A uniform dead load of 200 plf is applied at the top of
the wall. The footing below the piers is extended across the full length of the wall line
and is used as the continuous foundation, as shown in Fig. 13.12 and as referenced in IBC
Fig. 2308.9.3.2. It has already been determined that the foundation section at the opening
is not rigid. A computer model consisting of a wood frame on a semirigid foundation
has been used to determine the moments at the bases of the piers. The computer model
created a condition of partial fixity at the base of the piers. The soil pressures will actually
vary across the wall line similar to that shown in the figure. However, for this example,
the footing shown in the figure will be assumed to form hinges at the opening and
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